There’s a big controversy around certain bioplastics. This is because, a lot of the time, bioplastics aren’t as great as they seem. In fact, a lot of these products are greenwashed. Despite them being somewhat better than plastic in their ability to break down, some are not as sustainable as you might expect.
What is PLA?
The most popular bioplastic is made from polylactic acid, also called polylactide, and otherwise known as PLA. PLA is a biodegradable form of thermoplastic, produced from renewable sources such as sugarcane, cassava roots, and corn starch as opposed to common thermoplastics that are petroleum-based.
This kind of plastic has gotten the industry booming and is already quickly growing in widespread use. It is typically used for plastic films, bottles, cups, lids, cutlery, and the list goes on and on. There’s a lot of hype around PLA bioplastic, but it’s far from perfect.
How is PLA Made?
PLA is a polyester produced through fermentation under controlled conditions of a source of carbohydrate. Polymerization and condensation are two common methods of synthesis.
Polymerization, also called ring-opening polymerization, begins by dehydrating a lactic acid or lactide monomer at high temperatures for a few hours which creates prepolymer chains made of oligomers and PLA low in molecular weight. The system is heated so that the lactide produced can be recovered by distillation and gathered in a condensate flask, which is then mixed with various metal catalysts, typically tin octane, to form larger PLA molecules.
Condensation uses lactide as an “intermediate state”, resulting in larger molecular weight. The difference between this method and polymerization is the temperature and by-products released post-reaction, which are condensates. This approach is performed at less than 200°C where lactic acid is oligomerized to PLA oligomers, followed by poly-condensation. The result is short oligomers combining and producing high molecular weight PLA.
The complete composting process takes 1 to 6 months for PLA in an industrial composting facility, and this is massively dependent on high temperatures. Where composting PLA products takes around 6 months at home, it takes 1–3 in industrial facilities. However, the ability for PLA to be composted is not always leveraged. Most of it ends up in landfills instead because transfer stations responsible for sorting municipal waste find it difficult to sort PLA and PET as they share similarities like transparency.
Buyers generally offer lower prices or do not purchase the recycled material in case PLA contaminates waste streams. Because PLA is not 100% compostable, compost that contains PLA residue does not meet the Organic Materials Review Institute requirements, which all compost must follow in the USA. Thus, many composters think of PLA as a contaminant.
PLA has numerous benefits, which is why it’s becoming used on such a large scale. Its physical and chemical properties provide applications in packaging, medical devices like stents, dyeing textiles — even diapers! PLA is known for its excellent barrier properties, as well as its mechanical strength, resistance to chemicals and UV light, low flammability, and overall aesthetic purposes.
Another big perk — PLA can be 3D printed with ease. In fact, it is one of the most popular materials used in desktop 3D printing because it can be printed at low temperatures (having a melting temperature of 180ºC) and does not need a heated bed, instead having the ability to be easily printed on cold surfaces. In general, PLA melts more easily because of its lower melting point than alternative fossil fuel-based plastics, making it easy to work with and less energy-intensive.
PLA’s unique characteristics are now allowing the bioplastic to occupy 10.3% of the raw material used in bioplastic production, being used as a replacement for conventional polymers like polystyrene, polypropylene, and ABS. Of course, this is also more beneficial to the environment than traditional counterparts — but is the environmental impact the depiction of how it’s advertised?
The big problem with PLA is that there is quite a bit of greenwashing involved. People are often confused — is this a sustainable product or not? It’s made from sustainable sources, so it must be, right? That’s what many are often led to believe, but it isn’t necessarily true. PLA’s attributes are often miscommunicated or marketed wrongly.
PLA can decompose, yes, but only under specific aerobic conditions. As briefly mentioned earlier, PLA can degrade much faster than traditional plastics in industrial composting, but this isn’t where the majority of plastic goes. Not to mention it’s difficult to compost PLA industrially because of a lack of infrastructure in many places. Instead, the PLA has to decompose in the open and this can take around 80 years, having the same effects of being a pollutant on the environment.
PLA will decompose into water and CO2 in a matter of 47–90 days, but again, for this to happen, certain conditions have to be achieved. High temperatures of 140ºC paired with sunlight are necessary, and when plastic is shoved at the bottom of a landfill or in the ocean (PLA is not buoyant, so it sinks), these just cannot be achieved. PLA also needs to be exposed to special digestive microbes, and you can imagine how attaining this environment around the world could be hard.
There are additionally acidity and toxicity factors to consider. Since PLA is an acid, it raises the acidity of its surroundings as it composts, having the potential to pollute both land and ocean through acidifying nearby soil and water. This changes their pH and can take away valuable food supplies. Being toxic in nature is another danger if inhaled or absorbed by humans in the manufacturing process, therefore PLA must be carefully handled, especially during the molten formation step in the production process.
Lastly, there’s the issue of cost. PLA is not a complete alternative for petroleum-based bioplastics because the production process is still fairly expensive. There has been a surge in demand and subsequent supply shortage, leading to increased prices, which will need to be further looked into.
PLA is somewhat sustainable and a better alternative to fossil-fuel-derived plastic because of the ingredients and possibility of biodegradation — however, it still has its downsides and will not serve as an ultimate solution to the plastic pollution crisis.
Here’s an overview of what we learned!
- PLA is a biodegradable form of thermoplastic, produced from renewable sources
- PLA is created through fermentation, the two main methods being polymerization and condensation
- PLA is technically compostable but it has to be brought to composting facilities to biodegrade
- PLA has unique properties and can be 3D printed making it very useful for a variety of applications
- PLA’s downsides include the fact that it can only decompose under super-specific conditions, as well as acidity, toxicity, and cost
Thank you so much for reading this! I’m a 15-year-old passionate about sustainability, and am the author of “Chronicles of Illusions: The Blue Wild”. If you want to see more of my work, connect with me on LinkedIn, Twitter, or subscribe to my monthly newsletter!